@Margaret543 I think it best, if declining a reservation, and the guest asks you why you declined, to be honest while still being polite and professional. Instead of telling him the dates were unavailable (some guests, if told this, will contact Airbnb when they see the dates still available on your calendar and complain, which could cause Airbnb to read you the riot act or suspend your listing, and if you block the calendar, you'll of course be losing potential appropriate bookings).
"To be honest, XX, I don't feel comfortable accepting a booking request from someone who makes no attempt to tell me a little about themselves and why they wish to book with me, especially when they have no reviews or verifications, instead just announcing when they'll arrive. Perhaps in the future you'll be a bit more communicative with someone whose home you'd like to share. Hosts appreciate that."
This would probably stop him from trying to book with you again and educate him on good guest-host communication. Or he might send back a nice, apologetic message that sets your mind at ease, although I'd be wary and inclined to decline, too, with a local with no reviews or proper verifications.
I recently had a very similar booking request message- "I'll be arriving at noon if all goes according to plan." But he had two reviews, both good, and some decent profile info, so I just messaged back asking if he had thoroughly read my listing description and reiterating the few things I feel guests should be aware of regarding my offering, saying I'd be happy to accept his booking if he could confirm those things. He responded right away, indicating that he was aware of all, and telling me why he was comng to the area. In other words, the message he should have sent in the first place. He turned out to be a very sweet guy and a good guest.